The long term objective of this program is to find novel treatments for the mood disorders associated with cocaine withdrawal. A major problem with cocaine abuse is the return to cocaine use after a period of abstinence (relapse). contributing factor to cocaine relapse is withdrawal-induced anxiety and depression which stimulate re-administration as form of self-medication. Withdrawal from cocaine results in supersensitivity of serotonin-2A (5-HT2A ) receptors. 5-HT2A receptor supersensitivity is associated with depression and anxiety. Therefore, treating 5-HT2A receptor supersensitivity may alleviate the anxiety and depression that contribute to cocaine relapse. However, to date, no studies have investigated the mechanisms responsible for cocaine-induced 5-HT2A receptor supersensitivity. The proposed studies will investigate the mechanisms through which withdrawal from cocaine induces supersensitivity of 5-HT2A receptor-mediated secretion of hormones. In addition, two potential therapeutic approaches will be tested to reverse the supersensitivity of post-synaptic 5-HT2A receptors during cocaine withdrawal. Our hypothesis is that the cocaine-induced changes in sensitivity of 5-HT2A receptors are due to changes in specific components of the intracellular signaling cascade. The proposed studies will investigate signaling mechanisms underlying the supersensitivity of 5-HT2A receptor systems in the hypothalamic paraventricular nucleus after withdrawal from cocaine and their response to treatment. Aim 1 will determine the minimum number of cocaine injection days that will produce supersensitivity of 5-HT2A receptor signaling. One of the characteristics of drug dependence is that a drug must be administered repeatedly before withdrawal effects appear. Aim 2 will determine the onset of supersensitivity of 5-HT2A receptors after exposure to cocaine and to determine whether these effects are irreversible. This study also will establish the treatment parameters to be used in aims 3-4. The cocaine withdrawal effect may be a compensatory supersensitivity of 5-HT2A receptors due to reduced 5-HT release. Thus, Aim 3 will determine how the cocaine withdrawal effects on 5-HT2A receptors can be reversed by increasing the levels of 5-HT in the synapse with selective monoamine oxidase-A (MAO-A) inhibitors. Aim 4 will determine how the cocaine withdrawal effects on 5-HT2A receptors can be reversed by 5-HT2A antagonists. Our results from these studies on the treatment with selective 5-HT2A antagonists and MAO-A inhibitors may lead to novel therapeutic approaches to reverse the supersensitivity of 5-HT2A receptors and hence treat mood disorders associated with cocaine withdrawal and relapse.